Convergent regulation by ciliary neurotrophic factor and dopamine of tyrosine hydroxylase expression in cultures of rat substantia nigra

Circadian peak dopaminergic activity response at the biological clock pacemaker (suprachiasmatic nucleus) area mediates the metabolic responsiveness to a high-fat diet

Among vertebrate species of the major vertebrate classes in the wild, a seasonal rhythm of whole body fuel metabolism, oscillating from a lean to obese condition, is a common biological phenomenon. This annual cycle is driven in part by annual changes in the circadian dopaminergic signalling at the suprachiasmatic nuclei (SCN), with diminution of circadian peak dopaminergic activity at the SCN facilitating development of the seasonal obese insulin-resistant condition. The present study investigated whether such an ancient circadian dopamine-SCN activity system for expression of the seasonal obese, insulin-resistant phenotype may be operative in animals made obese amd insulin resistant by high-fat feeding and, if so, whether reinstatement of the circadian dopaminergic peak at the SCN would be sufficient to reverse the adverse metabolic impact of the high-fat diet without any alteration of caloric intake. First, we identified the supramammillary nucleus as a novel site providing the majority of dopaminergic neuronal input to the SCN. We further identified dopamine D2 receptors within the peri-SCN region as being functional in mediating SCN responsiveness to local dopamine. In lean, insulin-sensitive rats, the peak in the circadian rhythm of dopamine release at the peri-SCN coincided with the daily peak in SCN electrophysiological responsiveness to local dopamine administration. However, in rats made obese and insulin resistant by high-fat diet (HFD) feeding, these coincident circadian peak activities were both markedly attenuated or abolished. Reinstatement of the circadian peak in dopamine level at the peri-SCN by its appropriate circadian-timed daily microinjection to this area (but not outside this circadian time-interval) abrogated the obese, insulin-resistant condition without altering the consumption of the HFD. These findings suggest that the circadian peak of dopaminergic activity at the peri-SCN/SCN is a key modulator of metabolism and the responsiveness to adverse metabolic consequences of HFD consumption.

Kidney Cografts Enhance Fiber Outgrowth from Ventral Mesencephalic Grafts to the 6-Ohda–Lesioned Striatum, and Improve Behavioral Recovery

Recent studies have demonstrated the presence of many different neurotrophic factors in the developing and adult kidney. Due to its production of this mixture of neurotrophic factors, we wanted to investigate whether fetal kidney tissue could be beneficial for neuritic fiber growth and/or cell survival in intracranial transplants of fetal ventral mesencephalic tissue (VM). A retrograde lesion of nigral dopaminergic neurons was performed in adult Fischer 344 male rats by injecting 6-hydroxydopamine into the medial forebain. The animals were monitored for spontaneous locomotor activity in addition to apomorphine-induced rotations once a week. Four weeks following the lesion, animals were anesthetized and embryonic day 14 VM tissue from rat fetuses was implanted stereotaxically into the dorsal striatum. One group of animals received a cograft of kidney tissue from the same embryos in the same needle track. The animals were then monitored behaviorally for an additional 4 months. There was a significant improvement in both spontaneous locomotor activity (distance traveled) and apomorphine-induced rotations with both single VM grafts and VM–kidney cografts, with the VM–kidney double grafts enhancing the motor behaviors to a significantly greater degree. Tyrosine hydroxylase (TH) immunohistochemistry and image analysis revealed a significantly denser innervation of the host striatum from the VM–kidney cografts than from the single VM grafts. TH-positive neurons were also significantly larger in the cografts compared to the single VM grafts. In addition to the dense TH-immunoreactive innervation, the kidney portion of cografts contained a rich cholinergic innervation, as evidenced from antibodies against choline acetyltransferase (ChAT). The striatal cholinergic cell bodies surrounding the VM–kidney cografts were enlarged and had a slightly higher staining density for ChAT. Taken together, these data support the hypothesis that neurotrophic factors secreted from fetal kidney grafts stimulated both TH-positive neurons in the VM cografts and cholinergic neurons in the host striatum. Thus, these factors may be combined for treatment of degenerative diseases involving both dopaminergic and cholinergic neurons.

Effect of a ciliary neurotrophic factor polymorphism on schizophrenia symptom improvement in an iloperidone clinical trial

AIMS

Presence of the null FS63TER allele of the rs1800169 polymorphism in the gene encoding the ciliary neurotrophic factor (CNTF) may increase the risk of schizophrenia. This study prospectively evaluated the CNTF rs1800169 genotype (G/G vs non-G/G) effects on response to iloperidone.

PATIENTS & METHODS

Iloperidone 24 mg/day was evaluated in a study of patients with schizophrenia. Efficacy measurements included Positive and Negative Syndrome Scale total (PANSS-T), Brief Psychiatric Rating Scale (BPRS) and Clinical, Global, Impression (CGI) scores. The step-down primary end point was the difference in PANSS-T scores based on CNTF rs1800169 G/G genotype.

RESULTS

This study genotyped 417 patients (279 iloperidone and 138 placebo) for the rs1800169 polymorphism. Iloperidone significantly improved PANSS-T, PANSS positive subscale (PANSS-P), PANSS negative subscale (PANSS-N), BPRS, Clinical Global Impression of Change (CGI-C) and Clinical Global Impression of Severity (CGI-S) scores versus placebo. G/G versus non-G/G patients had greater improvement with iloperidone versus placebo in PANSS, BPRS and CGI scores.

CONCLUSIONS

The relative treatment benefit of iloperidone compared with placebo in patients with schizophrenia is enhanced in patients homozygous G/G for the rs1800169 polymorphism.

(-)-Stepholidine promotes proliferation and neuronal differentiation of rat embryonic striatal precursor cells in vitro

The present study investigated the influence of (-)-stepholidine, an effective dopamine D1 receptor agonist and D2 receptor antagonist, on the development of neural precursor cells. Incubation of striatal neural precursor cells with stepholidine resulted in significant increase in the number of proliferating precursor cell spheres when in the presence of fibroblast growth factor-2. This action can be blocked by application of haloperidol. Treatment with stepholidine also increased the number of microtubule-associated protein-2-immunoreactive cells in the cultures and promoted marked increases in tyrosine hydroxylase expression. These findings suggest that stepholidine is involved in the regulation of proliferation of precursor cells. The effect appears to be mediated by dopamine receptors. Stepholidine also promotes the differentiation of precursor cells, however, this action may be independent of its effect on dopaminergic receptors.

Apomorphine induces trophic factors that support fetal rat mesencephalic dopaminergic neurons in cultures

Apomorphine, the catechol-derived dopamine D1/D2 receptor agonist, is currently in use as an antiparkinsonian drug. It has previously been reported that apomorphine was able to elicit expression of the enzyme tyrosine hydroxylase, a marker for DA neurons, in the fetal rat cerebrocortical cultures whilst in the presence of brain-derived neurotrophic factor. The present study demonstrated that treatment of fetal rat ventral mesencephalic cultures with apomorphine caused a marked increase in the number of dopaminergic neurons. The action of apomorphine can be mimicked by dopamine receptor (D1 and D2) agonists or blocked by preincubation with D1/D2 receptor antagonists. Incubation of recipient mesencephalic cultures with the conditioned medium derived from apomorphine-stimulated donor mesencephalic cultures elicited a 3.72-fold increase in the number of TH-positive neurons. Increased mRNA expression levels of brain-derived neurotrophic factor and glial cell line-derived neurotrophic factor were also found in the apomorphine-treated mesencephalic cells along with concomitant protein expression increases in the conditioned medium. Moreover, the trophic activity observed could be partially neutralized by antibodies against either brain-derived neurotrophic factor or glial cell line-derived neurotrophic factor. Cultured fetal striatal cells, but not hippocampal cells, also responded to apomorphine treatment. The membrane filtration studies revealed that both <30 kDa and >50 kDa fractions contained trophic activities. The latter characterization distinguishes them from most known neurotrophic factors. These results suggest that the apomorphine-modulated development of dopaminergic neurons may be mediated by activation of the dopamine receptor subtypes D1 and D2 thereby increasing the production of multiple growth factors.

Prospects for the treatment of Parkinson's disease using neurotrophic factors

Parkinson's disease (PD) is a debilitating neurodegenerative condition that is characterised by a progressive loss of dopaminergic neurones of the substantia nigra pars compacta (SNpc) and the presence of alpha-synuclein cytoplasmic inclusions (Lewy bodies). Cardinal symptoms include tremor, bradykinesia, and rigidity, although cognitive and autonomic disturbances are not uncommon. Pharmacological treatment targeting the dopaminergic network is relatively effective at ameliorating these symptoms, especially in the early stages of the disease, but none of these therapies are curative and they generate their own problems. As dopaminergic neuronal death in PD occurs in a gradual manner, it is amenable to treatments that can either protect remaining dopaminergic neurones or prevent death of those neurones that have begun to die. Use of neurotrophic factors is a potential candidate, as various factors have been shown to increase dopaminergic neuronal survival in culture and promote survival and axonal growth in animal models of PD. Glial cell line-derived neurotrophic factor (GDNF) is currently the most effective substance that has been intensively studied and shown to have a specific 'dopaminotrophic' effect. This review will therefore focus on studies that have investigated GDNF and discuss the potential for neurotrophic factor treatment in PD.

Neurotrophic requirements of rat embryonic catecholaminergic neurons from the rostral ventrolateral medulla

The factors that regulate the ontogeny and differentiation of C1 adrenergic neurons located in the rostral ventrolateral medulla (RVLM) are completely unknown. In the present study, we have investigated the effects of a number of neurotrophic factors on the survival of E18-19 rat C1 adrenergic neurons in culture. Immunohistochemistry and reverse transcription polymerase chain reaction (RT-PCR) were used to study the expression of tyrosine hydroxylase (TH), an enzyme present in all catecholaminergic neurons, and of phenylethanolamine N-methyltransferase (PNMT), the final enzyme in the synthesis of adrenalin, as markers for the C1 RVLM neurons. Our results show that GDNF, CNTF BDNF, NT-3 and NT-4/5 increase the number of TH-immunoreactive neurons surviving in vitro. The effects of NGF, TGFbeta and bFGF were not significant. The E18-19 C1 neurons appeared to loose their ability to express PNMT in culture as examined with immunocytochemistry and RT-PCR, and none of the tested neurotrophic factors was able to sustain or induce this expression. Our results indicate that the adrenergic phenotype of C1 neurons, or the survival of these neurons, is determined by environmental factors other than the neurotrophic factors examined in this study.

Therapeutic potential of nerve growth factors in Parkinson's disease

Parkinson's disease (PD) is a neurodegenerative syndrome which primarily affects dopamine-producing neurons of the substantia nigra, resulting in poverty and slowness of movement, instability of gait and posture, and tremor at rest in individuals with the disease. While symptoms of the disease can be effectively managed for several years with available drugs, the syndrome is progressive and the efficacy of standard drugs wanes with time. One experimental approach to therapy is to use natural and synthetic molecules which promote survival and growth of dopaminergic neurons, so-called 'neurotrophic factors', to stabilise the diminishing population of dopaminergic neurons and stimulate compensation and growth in these cells. In this review, we examine the available evidence on 29 molecules with neurotrophic properties for dopaminergic neurons. The properties of these molecules provide ample reasons for optimism that a neurotrophic strategy can be developed that would provide a significant treatment option for patients with PD. While the search continues for even more specific, potent and long lasting agents, the single greatest challenge is the development of techniques for targeted delivery of these molecules.

Activity-dependent regulation of dopamine content in the olfactory bulbs of naris-occluded rats

Several lines of evidence strongly suggest that reduced olfactory nerve activity results in decreased bulb dopamine content. In the present study, high performance liquid chromatography with electrochemical detection was used to assess catecholamine levels in bulbs from postnatal day 60 rats that had undergone either unilateral naris cautery or a sham surgery on day 30. Thirty days of odor deprivation dramatically reduced dopamine and dihydroxyphenylacetic acid levels in functionally-deprived bulbs (ipsilateral to occluded nares) as compared to contralateral controls, while norepinephrine and dihydroxyphenylglycol levels were unchanged. The loss of dopamine was more severe in medial as compared to lateral aspects of experimental bulbs, while the loss of dihydroxyphenylacetic acid was similar on the two sides. To test directly the hypothesis that afferent activity regulates dopamine and dihydroxyphenylacetic acid content, 1 h of high frequency tetanic nerve stimulation was provided to the rostral-medial olfactory nerve layer in deprived olfactory bulbs, and catecholamine levels were assessed from 6 to 192 h later. Partial and temporary recovery of dopamine was observed in medial aspects of the bulb when rats were examined 96 h later, while consistent recovery of dihydroxyphenylacetic acid content was not apparent. These data corroborate evidence that olfactory nerve activity is a potent regulator of bulb dopamine and indicate that continued afferent input is necessary to maintain dopamine levels.

D1-dopamine receptor binding and tyrosine hydroxylase-immunoreactivity in the fetal and neonatal hamster suprachiasmatic nucleus

The suprachiasmatic nucleus (SCN) of the anterior hypothalamus is the site of an endogenous biological clock that regulates mammalian circadian rhythms. Circadian rhythms, although endogenously driven, are synchronized or entrained to daily environmental cues. Developmentally, the SCN begins to oscillate before birth and is entrained to the maternal circadian rhythm by a mechanism that is still unclear. Recent evidence in rats and hamsters suggests that a fetal dopaminergic system and D1-dopamine receptors may be involved in the process of entraining the fetal clock. The present study using [3H]SCH 23390 autoradiography and tyrosine hydroxylase (TH) immunocytochemistry determined the developmental time courses of the appearance of D1 receptor in, and catecholaminergic input to, the hamster SCN. [3H]SCH 23390 binding to D1-dopamine receptors was first detected in the fetal SCN on embryonic day (E) 15, the day before birth in this species, and persisted through adulthood. The TH immunoreactive fibers were first observed on day E15 coursing just ventral to the fetal SCN but TH-immunoreactive cells and fibers were not seen within the SCN until postnatal day (P) 5. The presence of D1-dopamine receptor binding in the fetal hamster SCN is consistent with the role of these receptors in entrainment of the fetal circadian pacemaker to maternal cues. However, a receptor-transmitter mismatch exists between D1-dopamine receptors and TH-immunoreactive fibers in the fetal SCN suggesting that the role of dopamine in maternal-fetal entrainment may be as a paracrine or humoral signal.

Nerve growth factors and the control of neurotransmitter phenotype selection in the mammalian central nervous system

Determination of neurotransmitter phenotype in the peripheral nervous system (PNS) has been intensively characterized. However, relatively little is known about the underlying molecular and biochemical events involved in determination of transmitter phenotype in the central nervous system (CNS). It has been well established that nerve growth factors regulate cell growth and differentiation. They are increasingly recognized as playing an important role in many decision-making steps during development. Published data suggest that neurotransmitter phenotype is determined largely by exogenous stimuli, such as nerve growth factors--acidic/basic fibroblast growth factor, epidermal growth factor, neurotrophins, etc., working in concert with the genetic programmes. They exert potent effects independently or synergistically with other molecules by acting either on neural precursor cells or differentiated neuronal cells. However, the process of transmitter phenotype determination in the CNS is only beginning to be understood, with more uncharacterized substances, with considerable potency in this respect being reported and in need of isolation and further study. These studies will bring great advances in our existing knowledge of brain development and have potential value for the development of new treatments for neurodegenerative diseases.

Expression of ciliary neurotrophic factor receptor-alpha messenger RNA in neonatal and adult rat brain: an in situ hybridization study

Ciliary neurotrophic factor is a pleiotropic molecule thought to have multiple functions in the developing and adult nervous system. To investigate the role of ciliary neurotrophic factor in the developing and mature brain by defining putative target cells the expression of the ligand-binding alpha-subunit of the ciliary neurotrophic factor receptor was studied in neonatal and adult rat brains using a digoxygenin-labelled probe for in situ hybridization. Neuronal populations expressing ciliary neurotrophic factor receptor-alpha messenger RNA were found in many functionally diverse brain areas including the olfactory bulb (mitral cells and other neurons) neocortex (layer V) and other cortical areas (pyramidal cell layers in the piriform cortex and hippocampus, granule cell layer of the dentate gyrus) and distinct nuclei in the thalamus, hypothalamus and brainstem. In the latter, reticular nuclei and both cranial motor and sensory nerve nuclei showed intense hybridization signals in the neonatal brain. The nucleus ruber, substantia nigra pars reticularis, deep cerebellar nuclei and a subpopulation of cells in the internal granular layer of the cerebellum were also labelled. In many areas (e.g. in thalamic, midbrain and pontine nuclei) ciliary neurotrophic factor receptor-alpha expression became undetectable with maturation; however, there were other areas (e.g., olfactory bulb, cerebral cortex and hypothalamus) where expression was higher in the adult. The neuroepithelium of the neonatal rat displayed a highly selective expression of ciliary neurotrophic factor receptor-alpha in areas which are known to exhibit high rates of postnatal cell proliferation in the germinal zones. Generally, neurons which have been reported to respond to exogenous ciliary neurotrophic factor were labelled by the ciliary neurotrophic factor receptor-alpha probe. This was not the case, however, for striatal and septal neurons. The results of this study suggest that ciliary neurotrophic factor receptor-alpha ligands have even broader functions than previously thought, acting on different neuronal populations in the developing and mature brain, respectively.

Influence of cocaine on the JAK-STAT pathway in the mesolimbic dopamine system

Chronic exposure to cocaine produces characteristic biochemical adaptations within the rat ventral tegmental area (VTA), a brain region rich in dopaminergic neurons implicated in the reinforcing and locomotor-activating properties of cocaine. Some of these changes are mimicked by chronic ciliary neurotrophic factor (CNTF) infusions into the same brain area. We show in this study that chronic cocaine treatment regulates the signal transduction pathway used by CNTF specifically in the VTA. There is an increase in immunoreactivity of Janus kinase (JAK2), a CNTF-regulated protein tyrosine kinase, in the VTA after chronic but not acute cocaine administration. This increase is not seen in the nearby substantia nigra or several other brain regions studied. Furthermore, this increase in JAK2 is not seen after chronic administration of other psychotropic drugs and was not observed for JAK1. The increase in JAK2 levels is associated with an increased responsiveness of the system to acute CNTF infusion into the VTA, as measured by induction in this brain region of signal transducers and activators of transcription (STAT) DNA binding activity and of Fos-like proteins, two known functional endpoints of JAK activation. Double-labeling immunohistochemical studies show that JAK2 immunoreactivity in the VTA is enriched in dopaminergic and nondopaminergic cells, both of which exhibit increased JAK2 immunoreactivity after chronic cocaine treatment. These findings suggest a scheme whereby some of the effects of chronic cocaine on VTA dopaminergic neurons are mediated directly by regulation of the JAK-STAT pathway in these cells, as well as perhaps indirectly by regulation of this pathway in nondopaminergic cells.

Induction of dopaminergic neurotransmitter phenotype in rat embryonic cerebrocortex by the synergistic action of neurotrophins and dopamine

Neurotrophins, including nerve growth factor, brain-derived neurotrophic factor (BDNF), neurotrophin-3 (NT-3) and neurotrophin-4/5 (NT-4/5), have been shown to enhance survival and differentiation of a variety of central neuronal populations, such as those with the dopaminergic, cholinergic, GABAergic phenotype during development. In this paper we present evidence that BDNF, NT-3 and NT-4/5 acting synergistically with dopamine (DA) can artificially induce the full dopaminergic phenotype in rat fetal cerebral cortex which normally has very few dopaminergic neurons in adulthood. Thus, BDNF/DA, NT-3/DA, NT-4/DA elicited a great increase in the number of tyrosine hydroxylase (TH)-immunoreactive cells, which was up to 5-7% of total neuronal population in cultures of fetal rat cortical cells. This stimulatory effect was not dependent on glial proliferation, or on addition of serum to the culture. Pharmacological studies showed that dopamine receptors D1 and D2 were involved in this effect. The TH+ cortical cells possessed other biochemical phenotypic features of dopaminergic neurons. Thus, high-affinity DA uptake was elevated in cortical cultures treated with neurotrophin/DA. Also DA and 3,4-dihydroxyphenlacetic acid production was detected (5.42 +/- 1.24 and 13.72 +/- 2.84 pmol/dish respectively, zero in controls). This show the presence of functionally active TH, aromatic acid decarboxylase and monoamine oxidase. Neurotrophins/DA had no effect on noradrenergic phenotype expression by cortical fetal cells. Taken together, these results support the long-standing view that development of the central nervous system is determined not only by intrinsic genetic programmes, but also involves environmental influences such as the action of growth factors and extracellular neurotransmitter. In this case we report the effect of specific DA phenotype-inducing agents.

STAT proteins are activated by ciliary neurotrophic factor in cells of central nervous system origin

Neuropoietic cytokines, including ciliary neurotrophic factor (CNTF) and leukemia inhibitory factor (LIF), have survival effects on cells of the peripheral and central nervous systems (PNS and CNS). CNTF and LIF also produce differentiation in some cells of the PNS. We have shown previously that CNTF activates the signal transducers and activators of transcription (STAT) family of transcription factors, and that this signaling pathway may be one of several employed by CNTF to regulate the expression of the vasoactive intestinal peptide (VIP) gene in cells of the PNS (Symes et al.: Proc Natl Acad Sci USA 90:572-576, 1993; Symes et al.: Mol Endocrinol 8:1750-1763, 1994). To investigate the mechanisms of action of CNTF in the CNS, we have analyzed the activation of STAT proteins in a septal-derived cell line, SN48, and in primary CNS cultures. CNTF treatment of SN48 cells produces a sustained activation of Stat3. CNTF treatment of SN48 cells also activated transcription mediated by the VIP cytokine responsive element (CyRE) which contains a STAT binding site. Mutation of the STAT site in the CyRE attenuated transcriptional activation by CNTF, indicating the importance of STAT proteins to CNTF-dependent transcriptional activation of SN48 cells. In cultures of embryonic rat septum and other brain areas, in addition to Stat3, CNTF also activates Stat1. As in cells of the PNS and non-neuronal cells, the Janus kinase (Jak)-STAT pathway is activated in CNS cells by cytokines. The SN48 cell line may be valuable in further characterization of regulation of the Jak-STAT pathway by neuropoietic cytokines.

Ciliary neurotrophic factor receptor alpha mRNA in NB41A3 neuroblastoma cells: regulation by cAMP

Ciliary neurotrophic factor (CNTF) affects the in vitro and in vivo survival and differentiation of several classes of neurons by binding to the CNTF receptor alpha. We examined the possibility that intracellular cAMP can regulate CNTF receptor alpha mRNA levels in two neuronal cell lines that display cAMP-dependent process outgrowth. Dibutyryl cAMP did not affect CNTF receptor alpha mRNA levels in PC12 cells but elicited a dose- and time-dependent increase in NB41A3 cell CNTF receptor alpha mRNA levels. Forskolin similarly increased CNTF receptor alpha mRNA levels in NB41A3 cells. The data suggest that signal transduction mechanisms involving cAMP may 'crosstalk' with CNTF-initiated signal transduction in a cell type-specific manner and that CNTF receptor alpha expression is not generally linked to neuronal process outgrowth.

Glia-dependent neurotoxicity and neuroprotection in mesencephalic cultures

Dopaminergic neurotoxicities of 6-hydroxydopamine (6-OHDA) and the lipopolysaccharide (LPS) were compared in rat mesencephalic cultures plated on poly-L-lysine or on glial monolayers. In the neuron-enriched cultures plated on polylysine, 6-OHDA killed 89% of the tyrosine hydroxylase (TH)-immunopositive neurons, but LPS was not neurotoxic. Conversely, in mixed neuron/glial cultures, 6-OHDA killed only 27% of the TH-immunopositive neurons while LPS killed 70%. The mixed neuronal/glial mesencephalic culture offers a better in vitro model for studying possible mechanisms involved in Parkinson's disease.

Serum-free B27/neurobasal medium supports differentiated growth of neurons from the striatum, substantia nigra, septum, cerebral cortex, cerebellum, and dentate gyrus

Two fundamental questions about neuron cell culture were addressed. Can one serum-free medium that was developed for optimum growth of hippocampal neurons support the growth of neurons from other regions of the brain? Is the region specific state of differentiation maintained in culture? To answer these questions, we isolated neurons from six other rat brain regions, placed them in culture in B27/Neurobasal defined medium, and analyzed their morphology and growth dependence on cell density after 4 days in culture. Neuronal identity was confirmed by immunostaining with antibodies to neurofilament 200. Neurons from each brain region maintained distinctive morphologies in culture in the virtual absence of glia. Cells isolated from embryonic day 18 cerebral cortex by digestion with papain showed the same high survival as hippocampal neurons, e.g., 70% survival for cells plated at 160/mm2. At this age and density, neurons from the septum showed slightly lower survival, 45%. Survival of dentate granule neurons from postnatal day four brains was 30-40%, significantly lower, and relatively independent of plating density. This suggests an absence of dependence on trophic factors or contact for dentate granule neurons. Growth of cerebellar granule neurons isolated from postnatal day 7, 8, or 9 brains in B27/Neurobasal was compared to growth in BME/10% serum. Viability in serum-free medium at 4 days was much better than that in serum, did not require KCl elevated to 25 mM, and occurred without substantial growth of glia. Cerebellar granule neurons plated at 1,280 cells/mm2 were maintained in culture for three weeks with 17% of the original cell density surviving. Survival of cells isolated from embryonic day 18 substantia nigra was 50% at 160 cells/mm2 after 4 days, similar to that of striatum, but slightly less than hippocampal neuron survival. The dopaminergic phenotype of the substantia nigral neurons was maintained over 2 weeks in culture as judged by immunoreactivity with antibodies to tyrosine hydroxylase. During this time, immunoreactivity was found in the processes as they grew out from the soma. Together, these studies suggest that B27/Neurobasal will be a useful medium for maintaining the differentiated growth of neurons from many brain regions. Potential applications of a common growth medium for different neurons are discussed.

Inhibitors of type IV phosphodiesterases reduce the toxicity of MPTP in substantia nigra neurons in vivo

The neuropathology of Parkinson's disease is characterized by the degeneration of dopaminergic neurons in the substantia nigra. We have recently shown that the activation of protein kinase A improves the survival of dopaminergic neurons in culture and, furthermore, protects them from the dopaminergic neurotoxin, 1-methyl-4-phenylpyridinium ion (MPP+) in vitro. We have now analysed the potential of phosphodiesterase inhibitors to increase cAMP levels in dopaminergic neurons, to improve their survival in culture and to protect them from the toxicity of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) in vivo. Increasing intracellular cAMP with phosphodiesterase type IV-specific inhibitors enhanced the survival of dopaminergic neurons in culture. Inhibitors of other phosphodiesterase types were not active. In vivo, phosphodiesterase type IV inhibitors reduced the MPTP-induced dopamine depletion in the striatum of C57BL/6 mice. Furthermore, the loss of tyrosine hydroxylase-immunopositive neurons in the substantia nigra of these animals was diminished. After Nissl staining, a similar reduction of the MPTP-induced loss of neurons was observed in the substantia nigra. The protective effect of protein kinase A activation did not appear to be due to the blocking of MPP+ uptake into dopaminergic neurons. This was not decreased after treatment with forskolin or 8-(4-chlorophenylthio)-cAMP. Thus, protein kinase A regulates the survival and differentiation of dopaminergic substantia nigra neurons in vivo, implicating a therapeutic potential for substances which regulate cAMP turnover in these neurons.

Astrocytes retrovirally transduced with BDNF elicit behavioral improvement in a rat model of Parkinson's disease

Neurotrophic factors that improve the survival of specific neuronal types during development and after exposure to various neuronal insults hold potential for treatment of neurodegenerative diseases. In particular, brain-derived neurotrophic factor (BDNF) has been shown to exert trophic and protective effects on dopaminergic neurons, the cell type known to degenerate in Parkinson's disease. To determine whether increased levels of biologically produced BDNF affect the function or regeneration of damaged dopaminergic neurons, the effects of grafting astrocytes transduced with the human BDNF gene into the striatum of the partially lesioned hemiparkinsonian rat were examined. Replication deficient retroviruses carrying either human prepro-BDNF or human alkaline phosphatase (AP) cDNA were used to transduce primary type 1 astrocytes purified from neonatal rat cortex. In vitro, BDNF mRNA was expressed by BDNF transduced astrocytes (BDNF astrocytes), but not control AP transduced astrocytes (AP astrocytes), as determined by reverse transcription polymerase chain reaction (RT-PCR). The modified astrocytes were injected into the right striatum 15 days after partial lesioning of the right substantia nigra with 6-hydroxydopamine. Transplantation of BDNF astrocytes, but not AP astrocytes, significantly attenuated amphetamine-induced rotation by 45% 32 days after grafting. Apomorphine-induced rotation increased over time in both groups, but was not significantly different in the BDNF-treated group. The modified BDNF astrocytes survived well with non-invasive growth in the brain for up to 42 days. Although BDNF mRNA positive cells were not detected within the graft site using in situ hybridization, alkaline phosphatase immunoreactive (IR) cells were present in control graft sites suggesting that the retroviral construct continued to be expressed at 42 days. Analysis of the density of tyrosine hydroxylase (TH)-IR fibers showed no effect of BDNF on TH-IR fiber density in the striatum on the lesioned side. These findings suggest that ex vivo gene therapy with BDNF ameliorates parkinsonian symptoms through a mechanism(s) other than one involving an effect of BDNF on regeneration or sprouting from dopaminergic neurons.

Development of a culture system for pure rat neurons: advantages of a sandwich technique

Primary cell cultures were derived from the cerebral cortices of embryonic rats (E 17). Survival of the cultures under serum-free conditions was improved by creating a sandwich: a poly-D-lysine-coated coverslip with plated cells was placed upside down in plastic culture dishes. Neurite outgrowth was observed within three hours after plating, and a neuronal network was established after 24 hours. The viability of the neurons gradually decreased. However, the cells could be cultivated for up to 24 days. Under these conditions the contamination with non-neuronal cells was minimized to less than 5%, as evidenced by immunohistochemical methods using the well-established cell marker proteins: neuron-specific enolase (NSE) as neuronal marker, and vimentin and glial fibrillary acidic protein (GFAP) as astroglial markers. Returning the coverslip to a normal open face position led to cell death within 24 hours. In order to investigate the maturation and differentiation of the cultured nerve cells, we looked for synapse formation by staining the synaptic vesicle protein synaptophysin (p38). It could be immunostained after three days in vitro (DIV) only in the neuronal perikarya, in perikarya and axons after six DIV, and in varicosities and contact points between axon terminals and adjacent axons or perikarya after 10-12 DIV. It appears that this simple culture method, which (i) yields highly enriched (> 95%) neuronal cultures with more than 85% cells surviving after five days in vitro, (ii) the absence of non-neuronal cells and (iii) the good maturation/differentiation of the cells, may be useful for the study of the neurochemical, physiological or regulatory mechanisms involved in nerve cell development.

Brain-derived neurotrophic factor works coordinately with partner molecules to initiate tyrosine hydroxylase expression in striatal neurons

Previous studies demonstrated that the cooperative interaction of acidic fibroblast growth factor (aFGF) and a partner molecule could induce the novel expression of the catecholamine (CA) biosynthetic enzyme, tyrosine hydroxylase (TH) in striatal neurons [Du and Iacovitti, J. Neurosci., in press; Du et al., J. Neurosci., 14 (1994) 7688-7694; Iacovitti et al., submitted]. The present study demonstrates that in addition to aFGF, brain-derived neurotrophic factor (BDNF) is also capable of moderate levels of TH induction (30% TH+ striatal neurons) when administered at high concentrations (100 ng/ml). As with aFGF, BDNF's activity depended on its coupling to an appropriate partner molecule; the most potent of which were 10 microM dopamine (DA) and 50 microM mazindol. BDNF + DA-induced TH expression was first evident after at 12 h; peaked by 18 h and declined by 4 days in culture. Cyclohexamide eliminated nearly all and alpha-amanitin reduced by half the TH induction elicited by DA and BDNF; indicating that both de novo transcription and translation were required for increased expression. In contrast with aFGF and BDNF, other putative dopamine differentiation factors, such as glial-derived neurotrophic factor (GDNF) and ciliary neurotrophic factor (CNTF), were able to elicit barely detectable (10%) levels of TH induction, regardless of the partner molecule used. These studies suggest that aFGF and/or BDNF may work coordinately with partner molecules to initiate TH expression; while a number of factors including, CNTF and GDNF, may be involved in its subsequent modulation.

Effects of chronic activation of dopamine D-2 receptors in cultures of rat fetal dopaminergic neurons: indications for alterations in functional activity

In Parkinsonian patients, previously subjected to neuronal grafting therapy, the survival and functional status of dopaminergic grafts might be impaired by the concurrent pharmacotherapy with L-DOPA and/or dopamine (DA) D-2 receptor agonists. To test this hypothesis in vitro, we studied the effects of chronic DA D-2 receptor activation on the functional capacity of cultured fetal rat mesencephalic DA neurons, using the activity of tyrosine hydroxylase (TH) and the intracellular dopamine content as neurochemical parameters. In cellular extracts prepared from our cultures, TH activity (as determined by the release of 3H2O from 3H-[3,5] tyrosine) appeared to be tetrahydrobiopterin-, Fe2+, and temperature sensitive, while in intact cells, the catalytic activity of TH could be induced by K(+)-evoked depolarization in a Ca(2+)-dependent way. In contrast, no acute DA D-2 receptor mediated inhibitory effects could be demonstrated in intact cells, either when tested under basal or depolarizing conditions. Nevertheless, after chronic exposure to DA D-2 receptor agonists for 14 days clear differences were observed in the functional status of cultured fetal dopaminergic neurons. Thus, whereas the overall survival and basal TH activity of cultured fetal dopaminergic neurons remained virtually unaltered, the depolarization induced activation of TH was enhanced in agonist-treated cultures. Moreover, after long-term treatment for 14 or 21 consecutive days, the intracellular DA content of agonist treated cultures appeared to be higher, as compared to untreated controls. It is concluded that chronic activation of DA D-2 receptors may induce adaptive alterations in the functional activity of cultured fetal dopaminergic neurons.(ABSTRACT TRUNCATED AT 250 WORDS)

Protection and repair of the nigrostriatal dopaminergic system by GDNF in vivo

Glial-cell-line-derived neurotrophic factor (GDNF), a recently cloned new member of the transforming growth factor-beta superfamily, promotes survival of cultured fetal mesencephalic dopamine neurons and is expressed in the developing striatum. There have, however, been no reports about effects of GDNF in situ. We have used the dopaminergic neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), which produces parkinsonian symptoms in man, to determine whether GDNF might exert protective or regenerative effects in vivo in the adult nigrostriatal dopamine system in C57/B1 mice. GDNF injected over the substantia nigra or in striatum before MPTP potently protects the dopamine system, as shown by numbers of mesencephalic dopamine nerve cell bodies, dopamine nerve terminal densities and dopamine levels. When GDNF is given after MPTP, dopamine levels and fibre densities are significantly restored. In both cases, motor behaviour is increased above normal levels. We conclude that intracerebral GDNF administration exerts both protective and reparative effects on the nigrostriatal dopamine system, which may have implications for the development of new treatment strategies for Parkinson's disease.

Glial cell line-derived neurotrophic factor augments midbrain dopaminergic circuits in vivo

Recently, a novel glial cell line-derived neurotrophic factor (GDNF) has been identified, cloned, and shown to have potent survival- and growth-promoting activity on fetal rat midbrain dopaminergic neurons in cell culture. In this study, we document marked and long-lasting effects on adult rat midbrain dopaminergic neurons in vivo after intracranial administration. A single injection of this factor into the substantia nigra elicited a dose-dependent increase in both spontaneous and amphetamine-induced motor activity, and a decrease in food consumption, lasting 7-10 days. Using immunocytochemistry, we found sprouting of tyrosine hydroxylase-positive neurites towards the injection site, and increased tyrosine hydroxylase immunoreactivity of the ipsilateral striatum was produced by GDNF. There was also a marked and dose-dependent increase in dopamine turnover in the substantia nigra and striatum, and in ipsilateral dopamine levels in the substantia nigra. Little or no effects of GDNF were seen on norepinephrine or serotonin levels. The neurochemical changes on dopaminergic afferents persist for at least 3 weeks after a single intracranial injection of 10 micrograms. Taken together, these data suggest that this glial cell line-derived factor has a potent influence on adult rat dopamine neurons and may have a potentially important role as a trophic factor for these neurons.

Ciliary neurotrophic factor

Ciliary neurotrophic factor (CNTF) was first identified and partially purified from embryonic chick eye tissues. Subsequently, it was shown that CNTF is also present in large amounts in sciatic nerves of adult rats and rabbits, which led to its final purification and cloning. CNTF is not secreted by the classical secretory pathway involving the endoplasmatic reticulum and Golgi complex, but can be detected in high quantities within the cytoplasm of myelinating Schwann cells and astrocytes using immunohistochemistry. CNTF supports survival and/or differentiation of a variety of neuronal cell types including sensory, sympathetic, and motoneurons. Also, nonneuronal cells, such as oligodendrocytes, microglial cells, liver cells, and skeletal muscle cells, respond to exogenously administered CNTF, both in vitro and in vivo. During development, expression of CNTF is very low, if indeed it is expressed at all, and the phenotype of mice lacking endogenous CNTF after inactivation of the CNTF gene by homologous recombination suggests that CNTF does not play a crucial role for responsive cells during embryonic development. However, motoneurons are lost postnatally in mice lacking endogenous CNTF, suggesting that CNTF acts physiologically on the maintenance of these cells. The ability of exogenous CNTF to protect against motoneuron loss following lesion or in other animal models indicates that CNTF might be useful in the treatment of human motoneuron disorders, provided appropriate means of administration can be found.

Choroid coat extract and ciliary neurotrophic factor strongly promote neurite outgrowth in the embryonic chick retina

Previous studies have shown that extracts from the target optic tectum stimulate neurite outgrowth from retinal explants. The present study indicates that the choroid coat is an even richer source of retinotrophic activity. We thus studied the effects of recombinant rat ciliary neurotrophic factor (CNTF) on primary cultures of dissociated chick ciliary ganglion neurons and retinal explants for a comparison with choroid coat extract from the E18 chick. For our assays, E9 ciliary neurons were incubated in collagen gels and retinal explants were cultured on collagen gels with the addition of the trophic factors and maintained for two or four days. Survival of ciliary neurons per area as well as maximal neurite length in retinal cultures were determined. Growth responses occurred in a dose-dependent manner both to CNTF and choroid extract. Immunofluorescence examination of cells and developing processes showed 200 kdal neurofilament positivity demonstrating that the cells studied were neurons with neurites. It is concluded that a trophic activity of the choroid as well as the recombinant CNTF stimulate retinal neuron survival and neurite extension. The results suggest that CNTF may have developmental functions in the establishment of the visual pathways.

The stimulatory effect of brain-derived neurotrophic factor on dopaminergic phenotype expression of embryonic rat cortical neurons in vitro

Cells of embryonic (E12-16) rat cerebral cortex were cultured for 7 days in vitro (7DIV) in the presence of either brain-derived neurotrophic factor (BDNF), ciliary neurotrophic factor (CNTF), with or without dopamine (DA). Chronic treatment of cells with DA or BDNF alone increased (300% and 600%, respectively) the number of the cells that expressed tyrosine hydroxylase (TH). However, the combination of BDNF and DA treatment greatly increased the expression of TH in E14 cortical cells in a dose-dependent manner, to a much greater extent than DA or BDNF alone. This marked response due to treatment with both BDNF and DA was greater in cortical tissue from E12 embryos than that from E14 embryos. The combination of CNTF and DA also increased expression of the dopaminergic phenotype whilst CNTF alone was ineffective, but this effect was largely due to DA. No effect of DA, or of neurotrophic factors, was observed on cortical cells from E16 embryos under any of the treatment conditions. The present study reveals how chemical environment plays an important role in determining the final phenotype of cortical neurons during early periods in brain development. BDNF, but not CNTF, may influence the differentiation of fetal cortical cells towards a dopaminergic phenotype via a unique mechanism, different from that due to DA. This combination of nerve growth factor and neurotransmitter may be of general importance in phenotype determination in the early developmental stages of the nervous system.

The response of human and rat fetal ventral mesencephalon in culture to the brain-derived neurotrophic factor treatment

Brain-derived neurotrophic factor (BDNF) has been shown to increase the survival of dopaminergic neurons in rodent mesencephalic cultures. The mRNAs of BDNF and trkB receptor have been found to be expressed in the substantia nigra of rat. In this study, the action of BDNF was studied on the survival and transmitter-specific differentiation of dopaminergic neurons of fetal human CNS aged 9-10-week in vitro. Dopaminergic neuron viability and phenotypic expression were monitored by tyrosine hydroxylase (TH) immunohistochemistry and measurement of dopamine (DA) content with HPLC, respectively. After seven days of treatment with BDNF there were 2.2-fold greater number of TH+ neurons surviving than in untreated cultures. Although very low levels of DA were detectable in human tissue, considerable amounts of DA was found in the culture medium from around 13 days in vitro (DIV), indicating that DA in human fetal tissue tended to be synthesised and released into the incubation medium more readily than from cultured rat fetal tissue during the same period. The content of DA in the BDNF-treated cultures was approximately double that of untreated cultures after 7 days. In rat fetal tissue, the capacity of each TH+ neuron to produce DA was not changed in the BDNF-treated cultures (7 DIV) compared with control cultures, suggesting that BDNF does not up-regulate the production of DA but rather acts to reduce cell death rates. Ciliary neurotrophic factor (CNTF) treatment of rat mesencephalic culture failed to improve the period of survival of fetal dopaminergic neurons and had no effect on the production of DA in cultures.(ABSTRACT TRUNCATED AT 250 WORDS)

Neurite outgrowth from cultured CNS neurons is promoted by inhibitors of protein and RNA synthesis

We examined the effects of changes caused by the blocking of protein and RNA synthesis on neurite outgrowth from neurons of the central nervous system (CNS) in primary culture. Exposure to cycloheximide and actinomycin-D led to dramatic increases in the length of neurites in cultures of neurons from various rat or chick CNS regions. Inhibitor-induced neurite outgrowth was observed (1) from dopaminergic neurons in mixed cultures of the rat substantia nigra or (2) in pure cultures of rat and chick neurons grown on a polyornithine/laminin substratum. These results suggest that neurite outgrowth from CNS neurons is kept restricted, at least in culture, by the continuous production of a labile neurite-inhibiting protein intrinsic to the neurons, which rapidly decays following inhibition of protein or RNA synthesis.

Re-initiated growth from mature ventral mesencephalon: an in oculo transplant study of nigrostriatal co-grafts

The ability of mature dopaminergic neurons derived from ventral mesencephalon to re-initiate growth after making contact with a non-innervated target was studied using the intra-ocular grafting model. Foetal ventral mesencephalic tissue or brain stem including the locus coeruleus area was grafted to the anterior chamber of the eye. Two weeks, 6 weeks or 1 year after the first implantation, foetal striatal tissue was placed in contact with the nigral graft or grafted alone. The size of the transplants was measured through the cornea. The final size of the striatal grafts was significantly larger when placed alone than when co-grafted with 1-year-old or 6-week-old dopaminergic grafts. Striatum grafted together with 2-week-old nigra was larger than when grafted adjacent to mature substantia nigra, but not significantly so. Nerve fibre outgrowth into the iris from the nigral transplants did not increase after maturation, but the re-innervated area of the host iris progressively increased around the locus coeruleus grafts. Ingrowth of tyrosine hydroxylase (TH) immunoreactive nerve fibres into the striatal grafts was studied 6 weeks after the second implantation. TH immunohistochemistry revealed innervation of the striatal piece in all cases, except for the group where striatum alone was grafted. With the short survival time for co-grafts of 6 weeks, TH-positive nerve fibres innervated a larger volume, had a patchy appearance and the density was higher in striatum grafted to 2 week-old nigral transplants than that seen in striatal transplants grafted to mature nigral grafts. The patchy pattern of TH-immunoreactive nerve terminals was also seen in striatum co-grafted with 6-week-old or 1-year-old nigral transplants. No difference in striatal innervation volume was detected between those latter two groups. When striatum was implanted adjacent to mature ventral mesencephalon and grown together for 6 months--the longer survival time--the same dense TH-positive innervation as seen in striatum co-grafted with immature nigral tissue at the shorter survival time was found. Additionally, the nigral part of the co-grafts showed increased TH-immunoreactive nerve fibre density. In conclusion, dopaminergic neurites from mature ventral mesencephalic transplants can re-initiate growth if placed in contact with non-innervated striatal tissue. The nigral grafts do not progressively re-innervate the host iris, while locus coeruleus grafts do. The intra-ocular grafting model can be used to study the in vivo effects of trophic factors on mature dopaminergic neurons.

Ciliary neurotrophic factor (CNTF) promotes low-affinity nerve growth factor receptor and CD4 expression by rat CNS microglia

Ramified parenchymal microglia may provide immune surveillance in the nervous system and become activated in response to injury, showing increases in antigens found on macrophages, e.g. CD4 and MHCs. We investigated in adult rats the effects of a 2-week intraventricular infusion with ciliary neurotrophic factor (CNTF), a nervous system-associated cytokine, on microglia of the normal and injured corpus callosum. CNTF caused morphological changes, induced the expression of low-affinity nerve growth factor receptor and CD4 and increased the expression of complement receptor 3. Such changes were also observed after treatment of pure cultures of neonatal rat microglial cells with highly purified CNTF, suggesting a direct responsiveness to CNTF. Thus, endogenous astroglial and Schwann cell-derived CNTF may be an important component of the immune responses of the nervous system.

Ciliary neurotrophic factor as an injury factor

This article reviews recent evidence suggesting that endogenous ciliary neurotrophic factor may be involved in neural responses to injury, and discusses the possibility that ciliary neurotrophic factor could have therapeutic applications in a clinical setting. The functional relevance of ciliary neurotrophic factor in non-injury situations is also evaluated, with emphasis on its possible roles in embryonic development.

Ciliary neurotrophic factor prevents degeneration of adult rat substantia nigra dopaminergic neurons in vivo

We have investigated the neuroprotective effects of recombinant human ciliary neurotrophic factor (CNTF) for injured dopaminergic neurons of the adult rat substantia nigra compacta. Fourteen days after a unilateral transection of the nigrostriatal pathway two-thirds of the neurons (identified by retrograde labeling) had degenerated. In sharp contrast, 73% (a few cases, > 90%) of this cell loss was prevented by continuous infusion of CNTF close to the injured neurons. However, CNTF did not prevent the disappearance of the transmitter-synthesizing enzyme tyrosine hydroxylase. Thus, CNTF has potent neurotrophic effects for injured adult rat dopaminergic substantia nigra neurons, whose degeneration plays a major causative role in Parkinson disease.